The case, likely to result in a close decision, could profoundly affect the roughly $63 billion gray market, in which third parties import brand-name goods protected by trademark or copyright into the United States.

It also gives the court a chance to delineate copyright protections at the very time that products and information from international sources become much more freely available, whether in physical form or downloaded or otherwise available online. A ruling is expected by June.

At the center of the case is Supap Kirtsaeng, a Thai national who arrived in the United States to study math at Cornell University and the University of Southern California.

He subsidized his education by reselling textbooks through eBay Inc's website that family and friends had bought in Thailand and shipped to him.

Eight of the textbooks came from an Asian unit of John Wiley & Sons Inc, prompting the publisher to sue Kirtsaeng for copyright infringement.